Hyperbranched polymers are classified as dendritic polymers together with dendrimers. While related-art polymers generally have a string form, these dendritic polymers have a highly branched structure. Accordingly, these dendritic polymers have various characteristics in such respects as a respect of having a specific structure, a respect of having a nanometer size, a respect of being capable of forming surfaces retaining many functional groups, a respect of being rendered having a low viscosity compared to linear polymers, a respect of exhibiting a behavior like fine particles with little entanglement between molecules, and a respect of being capable of becoming amorphous with their solubility in a solvent controllable, so that expectations lie in practical applications utilizing these characteristics.
Particularly, it is the most remarkable characteristic of dentritic polymers to have a large number of terminal groups. The more the molecular weight is, the more the number of branched chains increases, so that the absolute number of terminal groups becomes larger as the molecular weight of dendritic polymers increases. In such a dendritic polymer having a large number of terminal groups, intermolecular interactions depend largely on the types of the terminal groups, resulting in variations in its glass transition temperature, solubility, thin film forming properties, or the like. Accordingly, such a dendritic polymer has characteristics which no general linear polymer has. Further, to such a dendritic polymer, reactive functional groups can be added as terminal groups with an extremely high density, so that its applications as, for example, a high sensitive scavenger for functional substances, a high sensitive multifunctional crosslinking agent, a dispersant for metals or metal oxides, or a coating agent are expected. Accordingly, in dendritic polymers, it becomes an important factor for the exhibition of characteristics of the polymer how the type of the terminal group is selected.
An advantage of the hyperbranched polymer over the dendrimer is in its simplicity for synthesis, which is advantageous particularly in an industrial production. Generally, while the dendrimer is synthesized by repeating protection and deprotection, the hyperbranched polymer is synthesized by a one-step polymerization of a so-called ABx type monomer having in one molecule thereof, a total of three or more substituents of two types.
As a synthesis method thereof, a method for synthesizing a hyperbranched polymer by a living radical polymerization of a compound having a vinyl group while having a photo-polymerization initiating ability, is known. For example, a synthesis method of a hyperbranched polymer by a photo-polymerization of a styrene compound having a dithiocarbamate group (see Non-Patent Documents 1, 2 and 3), and a synthesis method of a hyperbranched polymer having a dithiocarbamate group by a photo-polymerization of an acryl compound having a dithiocarbamate group (see Non-Patent Documents 4, 5 and 6) are known.
[Non-Patent Document 1]
    Koji Ishizu, Akihide Mori, Macromol. Rapid Commun. 21, 665-668 (2000)[Non-Patent Document 2]    Koji Ishizu, Akihide Mori, Polymer International 50, 906-910 (2001)[Non-Patent Document 3]    Koji Ishizu, Yoshihiro Ohta, Susumu Kawauchi, Macromolecules Vol. 35, No. 9, 3781-3784 (2002)[Non-Patent Document 4]    Koji Ishizu, Takeshi Shibuya, Akihide Mori, Polymer International 51, 424-428 (2002)[Non-Patent Document 5]    Koji Ishizu, Takeshi Shibuya, Susumu Kawauchi, Macromolecules Vol. 36, No. 10, 3505-3510 (2002)[Non-Patent Document 6]    Koji Ishizu, Takeshi Shibuya, Jaeburn Park, Satoshi Uchida, Polymer International 53, 259-265 (2004)